In recent years, it has been revealed that various diseases are caused by increased generation of active oxygen species in a living body. Thus, dynamic analyses of active oxygen species in vivo are important in clarifying causes, states, and the like of diseases. In the analyses of active oxygen species, a bio-imaging method using a fluorescent probe plays a predominant role. As fluorescent probes used for detecting hydrogen peroxide, compounds such as dichlorofluorescin (which is the reduced form of dichlorofluorescein), dihydrorhodamine 123, and Amplex Red represented by the following formulas, for example, have been developed, and such compounds have been used for various purposes. The fluorescence mechanism of these compounds is based on an oxidation reaction caused by hydrogen peroxide in the presence of a peroxidase or a peroxidase-like enzyme.

However, not only hydrogen peroxide but also many kinds of active oxygen species serve as an oxidizing agent. Accordingly, it is considered that the above-described conventional fluorescent probes evaluate the total amount of oxidizing agents, including various oxygen species, generated in a living body rather than the amount of hydrogen peroxide generated in the same. Indeed, it has been reported that these probes respond to active oxygen species other than hydrogen peroxide (e.g., singlet oxygen, hydroxyl radicals, and peroxynitrite) and to various hemoproteins having oxidizing ability. Moreover, it has been pointed out that these probes might overestimate the amount of hydrogen peroxide because these probes generate hydrogen peroxide by being oxidized through air oxidation.
Also, there has been known a compound that generates a fluorescent compound not through a redox reaction but through a deprotection reaction caused by hydrogen peroxide. More specifically, acylated resorufin (a non-fluorescent compound) is transformed into resorufin as a fluorescent compound through a deprotection reaction caused by hydrogen peroxide (see Non-Patent Documents 1 and 2). However, such resorufin has a drawback in that it is subjected to a simple hydrolysis in a cell system so that it still cannot respond to hydrogen peroxide selectively.
Because of this, the development of a fluorescent probe that can respond to hydrogen peroxide with high selectivity has been demanded from the viewpoint of cytophysiology.    Non-Patent Document 1: H. Maeda, S. Matsu-ura, M. Nishida, T. Semba, Y Yamauchi, H. Ohmori, Chem. Pharm. Bull. 2001, 49, 294-298;    Non-Patent Document 2: H. Maeda, S. Matsu-ura, M. Nishida, Y Yamauchi, H. Ohmori, Chem. Pharm. Bull. 2002, 50, 169-174.